The present invention relates to electronic devices of the "bridge converter" type, which, supplied from an alternating network, are capable of supplying, at the output, a variable impedance load, such as a discharge lamp.
Known devices of this type are numerous and have been described, notably, in the following patents: PCT WO-83/00587; Europe 0,062,276; 0,075,176; 0,156,439 and 0,259,646; U.S. Pat. No(s). 4,104,715; 4,109,307; 4,184,128; 4,188,660; 4,382,212 and 4,700,287; Federal Republic of Germany 3112281; 3312575 and 3445817; Great Britain 2,061,037; France 76,31038 and 87,18567.
After having constructed and tested each of these devices for which the manufacture is sometimes complex, it has been inevitable to conclude that, for example, in the case of U.S. Pat. No. 4,109,307 or FR-87.18567, if the current taken from the network is strictly sinusoidal, on the contrary, the voltage applied at the output to the load is very strongly modulated by the rectified mains component.
In the case of certain others of these devices, inversely, this modulation of the output voltage is reduced by means of an electrolytic filtering capacitor which, in spite of the presence of a strong ferromagnetic input filter, brings about an unacceptable harmonic distortion of the mains current.
Thus, such apparatus do not allow an ideal interface to be provided between an alternating network and any load requiring a constant amplitude operating voltage without, for as much, affecting the sinusoidal nature of the input current such as its power factor.
Furthermore, such latter devices, by having recourse to an electrolytic smoothing capacitor can only offer an M.T.B.F. (mean time between failures) which is very limited and a reduced life at the operating temperatures of such a product.